In 2012, Shintaro Yamada was 34 years old, single and frustrated with his job. So he quit a comfortable position in Tokyo and set out to see the world.

He made a point of traveling on the cheap and mixing with the locals. He stayed at $5-a-night hostels without hot water, hitching motorbike rides and hopping on local buses between destinations. Over six months and 23 countries, he hiked the world's largest salt flat in Bolivia, stayed in a nomad's home at the edge of the Sahara desert, tracked the turtles of the Galapagos Islands and visited the tree in India where Buddha found nirvana.

The trip left him determined to start a company that would let people in different countries connect with each other. He saw that even the poorest villages had mobile phones and everyone craved technology for reaching the wider world. That led him to found Mercari Inc., a mobile e-commerce site that matches individual buyers and sellers and this month became the first Japanese startup worth at least $1 billion.